In the automotive industry, a by now consolidated choice is that of providing an automatic transmission as equipment for an increasingly larger number of automobiles. Of particular interest are transmissions that envisage the use of an electro-hydraulically or electromechanically actuated gearbox. Transmissions of the former type, which are more relevant to the invention in question, are represented by an embodiment provided by way of example in FIG. 1. In this figure, the reference number. 1 designates a gearbox of a known type proposed by the present applicant, which comprises a first casing 2 designed to house a clutch assembly, a second casing 4 designed to house the primary and secondary shafts of the gearbox (or, as in the case of the embodiment illustrated herein, to house the two primary shafts and the two secondary shafts, it being a double-clutch gearbox), and an electro-hydraulic actuation unit designated as a whole by the reference number 6.
The electro-hydraulic actuation unit 6 includes a plurality of valve assemblies that regulate the oil flow to hydraulic actuators so as to carry out the operations of selection and engagement of the forward and reverse gear ratios of the gearbox 1.
Co-operating with the electro-hydraulic unit 6 is a hydraulic pump 8, driven via an electric motor, which intakes oil from a tank 10 set at the top of the casing 4. The pump 8 intakes an oil flow from the tank 10 and delivers it to the valve assemblies within the unit 6 and, simultaneously, to an accumulator 11 and—through the control of the valve assemblies within the electro-hydraulic actuation unit 6—to a first hydraulic line 12 and a second hydraulic line 14 that each lead to an actuator device of a corresponding clutch.
A first actuator device designated by the reference number 13 receives fluid from the line 14 and is configured for actuation of a first clutch of the gearbox 1, whereas a second actuator device, which receives fluid from the line 12, is configured for actuation of a second clutch of the gearbox 1 but is set inside it and is not visible in the figure.
As is known, the provision of an electrically driven hydraulic pump is necessary since it enables maintenance of the supply of hydraulic fluid to the electro-hydraulic unit 6 and hence to the actuators that manage selection and engagement of the gears even in conditions of engine stop of the motor vehicle on which the gearbox 1 is installed, for example, as a consequence of activation of the so-called “start and stop” and “free wheel” functions.
The solution illustrated in FIG. 1, of a known type and proposed by the present applicant, is liable to present certain drawbacks. In particular, it has a certain number of hydraulic lines arranged externally with respect to the ensemble of the casings 2 and 4, which renders the system more exposed to risks of damage caused by the action of external agents. Furthermore, the components necessary for creating external hydraulic lines for pressurized fluid entail a non-negligible impact on the production costs.
In the second place, in the known solution illustrated, the unit 6 uses, as hydraulic fluid, an oil that is stored in a separate tank (the tank 10), which is located outside the casings 2 and 4 and is different from the one that provides for lubrication of the gearbox.
It is evident that in this way an additional component is required (the tank 10), as well as an additional operation of assembly of the tank itself, with consequent increase in the costs and need to adopt different solutions for handling and moving the gearbox 1 on a production line.
The ensemble of the above complications leads in practice to higher production costs and greater drawbacks during assembly and handling of the gearbox 1.
Furthermore, the known solution represented in FIG. 1 is suited in particular for use on gearboxes of the double-clutch type in which the clutch assembly is of the dry type.
The inventors have, however, noted that the layout of the electro-hydraulic actuation system of FIG. 1 is somewhat inconvenient in the case where it were to be applied to a gearbox, in particular of a double-clutch type, where the clutch assembly is of the multidisc, wet, type.